Microorganism-Based Larval Diets Affect Mosquito Development, Size and Nutritional Reserves in the Yellow Fever Mosquito Aedes aegypti (Diptera: Culicidae)

Abstract

Background: Mosquito larvae feed on organic detritus from the environment, particularly microorganisms comprising bacteria, protozoa, and algae as well as crustaceans, plant debris, and insect exuviae. Little attention has been paid to nutritional studies in Aedes aegypti larvae.

Objectives: We investigated the effects of yeast, bacteria and microalgae diets on larval development, pupation time, adult size, emergence, survivorship, lifespan, and wing morphology.

Materials and methods: Microorganisms (or Tetramin^® as control) were offered as the only source of food to recently hatched first instar larvae and their development was followed until the adult stage. Protein, carbohydrate, glycogen, and lipid were analyzed in single larvae to correlate energetic reserve accumulation by larva with the developmental rates and nutritional content observed. FITC-labeled microorganisms were offered to fourth instar larvae, and its ingestion was recorded by fluorescence microscopy and quantitation.

Results and discussion: Immature stages developed in all diets, however, larvae fed with bacteria and microalgae showed a severe delay in development rates, pupation time, adult emergence and low survivorship. Adult males emerged earlier as expected and had longer survival than females. Diets with better nutritional quality resulted in adults with bigger wings. Asaia sp. and Escherichia coli resulted in better nutrition and developmental parameters and seemed to be the best bacterial candidates to future studies using symbiont-based control. The diet quality was measured and presented different protein and carbohydrate amounts. Bacteria had the lowest protein and carbohydrate rates, yeasts had the highest carbohydrate amount and microalgae showed the highest protein content. Larvae fed with microalgae seem not to be able to process and store these diets properly. Larvae were shown to be able to process yeast cells and store their energetic components efficiently.

Conclusion: Together, our results point that Ae. aegypti larvae show high plasticity to feed, being able to develop under different microorganism-based diets. The important role of Ae. aegypti in the spread of infectious diseases requires further biological studies in order to understand the vector physiology and thus to manage the larval natural breeding sites aiming a better mosquito control.

Keywords: Aedes aegypti; algae; bacteria; development; digestion; microorganism; nutritional reserves; yeast.

FIGURE 1

The viability of microorganisms in water. Total counts of CFU after centrifugation of microbial cells suspended in liquid media, water and after keeping the resuspended cells in water for 120 h. Figures are means ± SEM of 15 experiments each. (T-Test; ^∗p > 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.005).

FIGURE 2

The impact of microorganism-based diets on pupation time. A representative pupation curve is comparing larvae fed with Tetramin (Dark blue line, left y-axis) and larvae fed with microbial cells (red line, right y-axis). The dietary supply was administered only at L1. Dead individuals were removed daily.

FIGURE 3

The impact of microorganism-based diets on adult emergence. A representative emergence curve is comparing larvae fed with Tetramin (Dark blue line, left y-axis) and larvae fed with microbial cells (red line, right y-axis). The dietary supply was administered only at L1. Dead individuals were removed daily.

FIGURE 4

The impact of microorganism-based diet on adult survival. A representative survival curve comparing larvae fed with Tetramin (Dark blue line, left y-axis) and larvae fed with microbial cells (red line. Right y-axis). The dietary supply was administered only at L1. Survival was assessed daily.

FIGURE 5

The impact of microorganism-based diets on total life span. A representative life span curve is comparing larvae fed with Tetramin (dark blue line, left y-axis) and larvae fed with microbial cells (red line, right y-axis). The dietary supply was administered only at L1. Survival was assessed daily.

FIGURE 6

Descriptive statistics of right (B,D,F,H) and left (A,C,E,G) wing centroid sizes (in mm) of males and females from different diets. (A–D) Comparison between control diet (Tetramin^®) and Gram-negative bacteria (Asaia sp. and E. coli). (E–H) Comparison between control diet [Tetramin (R)] and Yeasts (Pseudozyma sp. and S. cerevisiae). Vertical lines: individuals. Asterisks: Non-normal distribution.

FIGURE 7

Ae. aegypti larvae consume different microorganisms offered in diets. (A) Mean fluorescent intensity in the intestine of larvae 2 h after placement of FITC-labeled microorganisms into rearing water. Columns present mean values with 95% confidence intervals for each diet (ANOVA 1; ^∗p < 0.05; ^∗∗∗p < 0.001). Figures are means ± SEM of 5 experiments with ten larvae each. (B) Epifluorescent images of microscope slide glass with FITC-labeled E. coli (D31) and individual larva 2 h after placing FITC-labeled E.coli (D31) into the rearing water.